1. Field of the Invention
The present invention relates to a thermistor device including a flexible thermistor element.
2. Description of the Related Art
Conventionally, this kind of thermistor device is used for a temperature sensor or the like. This temperature sensor includes, as described in, for example, Japanese Patent Application Laid-Open No. 2000-266608, a heat-resistant resin sheet, two lead electrodes, a ceramic thermistor element, and an exterior sheet. The heat-resistant resin sheet is composed of polyimide of approximately 50 μm in thickness. The two lead electrodes are composed of a metallic material containing silver of approximately 10 μm in thickness. The two lead electrodes are formed by printing or the like on a principal surface of the heat-resistant resin sheet, so as to be spaced at a predetermined interval. The thermistor element is approximately 0.5 mm in thickness, and connected to one end of the two lead electrodes. The exterior sheet is composed of polyimide of approximately 50 μm in thickness. This exterior sheet covers the respective lead electrodes and the thermistor element. However, the other end of each lead electrode is exposed for connection to another circuit. The heat-resistant resin sheet and exterior sheet are closely attached and fixed with a heat-resistant adhesive.
In the use of the temperature sensor described above, the user fixes the thermistor element with an adhesive or the like onto an object to be detected such as, for example, a lithium ion battery. Then, in the temperature sensor, a voltage value that is correlated to the temperature of the object to be detected is output to the other end of the two lead electrodes.
However, the heat-resistant resin sheet and exterior sheet made of polyimide expand with the changes in the temperature of the object to be detected. In general, the resin (heat-resistant resin sheet and exterior sheet) expands more than the thermistor element. This expansion places stress on the connection parts between the thermistor element and each lead electrode. There has been a problem that this stress fractures the connection parts, or cracks the body of the thermistor element.